1. Field of the Invention
The present invention relates to a control apparatus for an internal combustion engine capable of controlling air-fuel ratio and ignition timing of an air-fuel mixture to be supplied to the internal combustion engine.
2. Discussion of Background
FIG. 17 is a schematic illustration showing an example of a control device for a conventional internal combustion engine. As shown in FIG. 17, fuel is sucked from the fuel tank 1 and pressurized in the fuel pump 2, the pulsation of which is stabilized by the fuel damper 3, the particles and the moisture of which are removed by the fuel filter 4, the pressure of which is made constant by the pressure regulator 5 and is supplied to the fuel injection valve 6.
The pressure regulator 5 makes the pressure of the fuel constant. For instance, the pressure of the fuel is made 2.5 kg/cm.sup.2 which is the pressure difference between the fuel pressure and a suction pressure of air. The part 7 is a cold start valve which injects fuel and which improves the starting-up of this engine in cold weather.
The quantity of air which passed through the air cleaner 8 is measured by the air-flow meter 9 and regulated by the throttle valve 10. The air passes through the suction manifold 11 and mixed with the fuel by the fuel injection valve 6 and send to each cylinder 12.
The mixture is compressed by the cylinder 12 and ignited by the ignition plug 13 at a pertinent timing.
Exhaust gas is exhausted in the air after it passes through the exhaust manifold 14 and a gas purifying device not shown. The part 40 is an exhaust gas sensor which detects the concentration of the exhaust gas, for instance the oxygen concentration.
The part 15 is a water temperature sensor which detects the temperature of cooling water of the engine. The part 16 is a crank angle sensor of the engine which is incorporated in a distributor. The part 17 is an ignition device. The parts 18 is a control device which controls an air-fuel ratio of the mixture to be supplied to the engine.
The crank angle sensor 16 generates a reference position pulse at every reference position of the crank angle (for example, every 180.degree. in a four cylinder engine and every 120.degree. in a six cylinder engine), and generates a unit angle pulse at every unit angle, (for example every 2.degree.). The crank angle can be shown in the control device 18 by counting the number of every unit pulse after the reference position pulse is generated.
The control device 18 is a microcomputer composed of for instance, a CPU, a RAM, a ROM, an I/O interface and so on. The control device 18 receives a suction air quantity signal S1 from the above-mentioned air-flow meter 9, a water temperature signal S2 from the water temperature sensor 15, a crank angle signal S3 from the crank angle sensor 16, an exhaust gas signal S10 from the exhaust gas sensor 40, a battery voltage signal, and a signal indicative of the throttle valve being fully closed although the signals are not shown in FIG. 17. The control device performs a calculation corresponding with these signals and calculates the quantity for fuel injection to be supplied to the engine, or the time of valve opening of the fuel injection valve 6, and outputs a fuel injection signal S5.
By this injection signal S5, the fuel injection valve 6 is put into motion once per every revolution of the engine and a predetermined quantity of fuel is supplied to the engine.
The calculation of a fuel consumption, or a fuel injection time T.sub.i is performed in the above-mentioned control device 18 by, for example, the following equation. This equation is described in a Nissan Technology guide book for 1979 ECCSL engines. EQU T.sub.i =T.sub.p .times.(1+F.sub.t +KMR/100).times..beta.+T.sub.s ( 1)
In equation (1), T.sub.p is the basic injection quantity or the basic valve opening time and is calculated by the following equation wherein Q signifies the suction air quantity per one revolution, N, the rpm of the engine, and K, a constant. EQU T.sub.p =K.multidot.Q/N
F.sub.t is a correction coefficient which corresponds to the temperature of the cooling water for the engine. The value is increased as the temperature of the cooling water is decreased, as shown in FIG. 16.
The above-mentioned suction air quantity Q is obtained from the signal S1 of the air-flow meter 9, N, from the signal S3 of the crank angle sensor 16, and F.sub.t, from the water temperature signal S2 of the water temperature sensor 15.
KMR is a correction coefficient in case of heavy load time. As shown in FIG. 15, the value is memorized in a data table corresponding with the basic injection quantity T.sub.p and the rpm of the engine N, and is read out from the table.
T.sub.s is a correction coefficient for the battery voltage which is a coefficient to correct the variation of a voltage that drives the fuel injection valve 6. The coefficient is for example, is obtained by the following equation, wherein V.sub.B is the battery voltage and a and b are constants. EQU T.sub.s =a+b (14-V.sub.B)
As shown in FIG. 14, the value increases as the battery voltage decreases.
.beta. is a correction coefficient corresponding with the exhaust signal S10 from the exhaust gas sensor 40. By using this .beta., the air-fuel ratio of the mixture can be controlled by a feed back control, to a predetermined value, for instance, a value in the neighborhood of a theoretical air-fuel ratio 14.8.
However, when this feed back control by the exhaust signal S10 is carried out, the air-fuel ratio is made always constant, which makes the above-mentioned corrections by the temperature of the cooling water or at the heavy load time meaningless.
Therefore the feed back control by the exhaust signal S10 is carried out, when the correction coefficient F.sub.t for water temperature or the correction coefficient KMR for heavy load time is zero.
Japanese Unexamined Patent Publication No. 59061/1982 discloses a control device for ignition timing of an internal combustion engine. This control device is of an electronic ignition timing control system. As shown in FIGS. 12 and 13, the value of the optimum ignition lead angle corresponding with the rpm of the engine N and the basic injection quantity T.sub.p is memorized in a data table. The control device read out the value which corresponds with the current revolution speed and the basic injection quantity, by looking up the table, and the ignition signal S6 is output to the ignition device 17 and the ignition plug 13 is activated so that the ignition timing is controlled to the above value.
However, in the conventional control device of the internal combustion engine the feed back control is carried out corresponding to the exhaust signal S10 from the exhaust sensor 40 and the correction in heavy load time is determined by the basic injection quantity and the revolutional speed, that is, by the suction air quantity and the revolutional speed, which is carried out by an open loop control.
Therefore, the control value is deviated from the point of LBT by the variation and the timewise change of the air-flow meter 9 or the fuel injection valve 6, and the torque of the engine is lowered and the stability of the engine is worsened as shown in FIG. 9. LBT is the abbreviation of the Leanest Mixture for Best Torque which is an air-fuel ratio that makes the value of the generated torque maximum. This value is different from the air-fuel ratio which is fed back by the aforementioned exhaust gas sensor signal.
Moreover, in the ignition timing control, the conventional control system is an open loop system wherein the ignition timing is read out from the data table memorized beforehand in carrying out the control. Therefore in this system, the ignition timing may be deviated from MBT which is initially matched but changed later by the variation and the timewise change of the engine itself, which causes the lowering of the torque of the engine or generation of knocking as shown in FIG. 10. MBT is the abbreviation of Minimum Spark Advance for Best Torque.
Furthermore, the above-mentioned fuel control and the ignition timing control are separately carried out, and no general control is carried out wherein the above two control systems are interrelated.
As shown in FIG. 11 which is a diagram for air-fuel ratio versus ignition timing characteristic, with respect to the relationship between the air fuel ratio control and the ignition timing control, as a condition which makes the generated torque of the engine maximum, the LMBT shown as a checked point in FIG. 11 realizes both the LBT and the MBT. However in the aforementioned conventional example, the fuel control and the ignition timing control are not interrelated.
Accordingly, the optimum control is not carried out in the conventional technology.